In current type switching power supply control, the peak current mode control is one of general control methods. It can be used in several switching power supplies control, e.g. constant turn-off time control and inductor current critical discontinuous control etc. In practical application, the inductor peak current mode control can't be controlled in high accuracy. In general, the control method is implemented with a comparator, that is, the detected inductor peak current is compared with a fixed reference signal level; as the detected inductor peak current is higher than the fixed reference signal level, the comparator turns from “1” into “0” and the power switch is turned off through switching power supply driving circuit. In the general control implement, the real inductor peak current isn't equal to the fixed reference signal level. There is a difference ΔiL between the real inductor peak current and the fixed reference signal level. It is impacted with several issues, the first is the inductor rising up slope; the second is the delay times Td and Tp of the comparator and switching power supply driving circuit; the third is the offset voltage of the comparator; the fourth is the comparator needs driving energy, that is, driving charge Q=ΔV*ΔTd/2. It is those issues that make the real inductor peak current variable with the input and output voltages of the switching power supply (as shown in FIG. 1). As the input voltage of the switching power supply increases, the inductor current rising up slope increases. For the fixed delay times Td and Tp of the comparator and switching power supply driving circuit, the difference ΔiL increases due to the slope of the inductor current. As the input voltage of the switching power supply decreases, the inductor current rising up slope decreases. For the fixed delay times Td and Tp of the comparator and switching power supply driving circuit, the difference ΔiL decreases due to the slope of the inductor current. It is clear that to decrease the difference ΔiL, the fixed delay times Td and Tp of the comparator and switching power supply driving circuit must be decreased. In practical application, it is very difficult to largely decrease the fixed delay times Td and Tp of the comparator and switching power supply driving circuit.
In most application of the current type switching power supply, it is required that the average output current should be independent of input and output voltages, e.g. in LED driving application, the accuracy of the output current is required under 5%. For step down DC-DC converter inductor current critical discontinuous control case, the average output current is half of the peak inductor current. In order to make the accuracy of the output current under 5%, it requires the accuracy of the peak inductor current under related level.